Heretofore, in electrolysis of brine, a diaphragm method in which an anode compartment and a cathode compartment are defined by a porous neutral diaphragm comprising asbestos or the like has been employed in place of the mercury method. This diaphragm method, however, has the disadvantage that it cannot be used to produce high quality alkali metal hydroxides. Thus, for electrolysis of brine to obtain high quality alkali metal hydroxides, a so-called ion exchange membrane method using a cationic exchange membrane has been developed.